1. Field the Invention
This invention relates to a still image signal processing device for recording a still image signal on a recording medium such as a floppy disc and for reproducing the still image signal recorded on the recording medium.
2. Description of the Related Art
In the conventional still image signal recording or reproducing apparatus of the kind using a video floppy disc (hereinafter referred to as a VF disc) as a recording medium, a motor control circuit has been arranged as shown in FIG. 1 of the accompanying drawings. Referring to FIG. 1, a video signal to be recorded or reproduced is inputted to an input terminal 101. At a synchronizing (hereinafter abbreviated to sync) signal separation circuit 102, a vertical sync signal (hereinafter referred to as a sync signal VD) is separated from the video signal. The sync signal VD is inputted to a phase-locked loop (hereinafter referred to as a PLL) 103. Meanwhile, a PG pin which is disposed at a VF disc 106 is detected by a PG detection circuit 107. The PG detection circuit 107 then supplies to the PLL 103 a pulse signal which is synchronized with the rotation of the VF disc 106. The PLL 103 outputs a signal reflecting a phase difference between the pulse signal and the sync signal VD.
The output signal of the PLL 103 is supplied to a driver 104. The driver 104 is arranged to output a driving signal under the control of the signal from the PLL 103 for causing a motor 105 to rotate the VF disc 106.
The rotation of the VF disc 106 is thus controlled to be in synchronism with the sync signal VD. When recording an ordinary interlaced video signal on the VF disc 106, one turn of the VF disc 106 takes a period of time 262.5 times as much as the horizontal synchronizing period (hereinafter referred to as "H") (in the NTSC system). In other words, according to this still image signal reproducing system (hereinafter referred to as "SV format"), a video signal of 262.5 H is recorded in each track which is arranged on the VF disc 106 to record the video signal for one field.
Two methods are used for recording a video signal on the VF disc 106, including a field recording method in which an amount of the video signal for one field is recorded in one track on the VF disc 106, and a frame recording method in which an amount of the video signal for one frame is recorded in two tracks, that is, in a recording area corresponding to two fields.
As for a method for reproducing the video signal thus recorded on the VF disc 106, there are two methods including a field reproducing method in which an image is reproduced from the video signal recorded in one track (a recording area for one field) on the VF disc 106, and a frame reproducing method in which an image is reproduced from the video signal recorded in two tracks (a recording area for two fields).
In order to reproduce by the field reproducing method the video signal recorded by the field recording method and to have the reproduced signal displayed as an image on a cathode-ray tube (hereinafter referred to as a CRT), the video signal must be converted into an interlaced video signal. Therefore, a circuit which is arranged as shown in FIG. 2 is included as a component element in a signal processing circuit which is arranged to perform various processes on the video signal reproduced from the VF disc 106. The video signal inputted from an input terminal 111 is outputted from an output terminal 115 through an amplifier 114 after the video signal is switched by every one field by a switch 113. More specifically, a video signal forming an odd-number field is allowed to be outputted without passing through a 1/2 H delay line 112, while another video signal forming an even-number field is outputted after being delayed by the 1/2 H delay line 112. The input video signal is thus converted into an interlaced video signal. This process is called a 1/2 H skew compensation.
If a noninterlaced video signal is to be recorded while controlling the motor 105 by means of the motor control circuit which is arranged as shown in FIG. 1, the recording track comes to deviate from the SV format, for the following reason: in that case, one field of the noninterlaced video signal is composed of a video signal of 262 H or 263 H. This video signal is inputted to the input terminal 101 of the control circuit of FIG. 1. The rotation of the VF disc 106 is then controlled to record the video signal of 262 H or 263 H, instead of 262.5 H, in one track on the VF disc 106. The recording track thus deviates from the SV format.
The problem can be solved by recording a 2-track amount of the noninterlaced video signal according to the frame recording method and by reproducing the same according to the frame reproducing method. In that case, the recorded signal can be correctly reproduced as the noninterlaced video signal, because the intervals of a horizontal sync signal (hereinafter referred to as a sync signal HD) are adequately maintained. However, in cases where the noninterlaced video signal which has been recorded by the field recording method is reproduced by the field reproducing method, the intervals of the sync signal HD come to vary every time one field is switched over to another because of the 1/2 H skew compensation made at the time of reproduction. This results in a turbulence of the reproduced image on the CRT.